The kidney is the main organ involved in the long term regulation of total body potassium. Disorders of potassium balance occur frequently in patients who have hypertension, congestive heart failure, cirrhosis of the liver and renal dysfunction. Hypokalemia causes significant cardiovascular morbidity and mortality in patients treated with diuretics. Furthermore, abnormal regulation of K channels may play a role in the pathogenesis of hypertension. This laboratory is focused on the study of renal potassium channels. This work has let to the discovery of several novel K channel genes. One of these genes encode a cGMP-activated, K-selective channel (KCNA 10a) which is expressed in kidney, heart, muscle and blood vessels. KCNA10a has kinetic properties similar to those of the nitric oxide sensitive K channels detected in pulmonary artery smooth muscle cells. The work now proposed is an extension of the original proposal. The investigative team has recently succeeded in optimizing KCNA10a current expression in Xenopus oocytes and are now able to study its kinetic properties of the single channel level in detail. They will then determine if it is a hetero-multimeric protein and if its expression levels and/or kinetic properties are modulated by any of the live previously cloned a subunits. They will investigate the regulation of KCNA10a by cGMP and ask whether cGMP activates by binding to the cGMP-binding domain and/or via protein phosphorylation. Finally, a panel of high affinity polyclonal antibodies specific for the KCNA10a protein will be developed in order to examine its tissue distribution and membrane localization. The intent is that studies already carried out and those that are proposed in the current application will provide insight into the mechanisms by which K balance is maintained and should, therefore, have direct clinical applications. It is also hoped that the discovery of new molecular structures will expand the existing physiological framework of potassium homeostasis and will lead to the development of new therapeutic agents.